Variable electrical resistances and potentiometers



Dec; 23, 1958 p. x. FOX 2,866,050

VARIABLE ELECTRICAL RESISTANCES AND POTENTIOMETERS Filed Oct. 11, 1954 My I 2 B LXAvmm Fox INVENTOQ United States Patent VARIABLE ELECTRICAL RESISTANCES AND POTENTIOMETERS Paul X. Fox, Horsforth, near Leeds, England Application October 11, 1954, Serial No. 461,592

3 Claims. (Cl. 20148) The present invention relates to adjustable electrical resistors, and more particularly to resistors of this character provided with a control shaft, wherein the incremental changes in resistance which result from any predetermined small angular displacement of the shaft are different for different positions of the shaft in accordance with a predetermined desired mathematical function such as a sine, cosine or other non-linear function.

The variable electrical resistance or potentiometer according to the present invention comprises an annular resistance element, a generally circular cam of nonuniform radius fixed coaxially with respect to said resistance element, a cam-follower co-operating with the circumference of said cam, a sliding contact member co-operating with said resistance element, a control shaft for causing relative rotary movement between said resistance element and said contact member, and means linking said cam-follower with said contact member, whereby the point of contact of the contact member with the resistance element is advanced or retarded in relation to the point at which contact would be made if the cam were truly circular, according to the shape of the circumference of the cam.

Conveniently, the annular resistance element and the cam are rotated together as a unit by the control shaft and the only movement applied to the contact member is the adjusting movement which produces the nonlinear resistance variation and which results from the engagement of the cam-follower with the specially shaped circumference of the cam.

In order that this invention may be more clearly understood and readily carried into effect, reference may be made to the accompanying drawings which illustrate, by way of example, one convenient embodiment of the present invention, and in which:

Figure 1 is a front elevation of the device;

Figure 2 is a section on line 2-2 of Figure 1;

Figure 3 is a section on line 22 of Figure 1 showing the position of the slidable contact member when it has been displaced from its mean position by the special shape of the cam; and

Figure 4 is a section on line 44 of Figure 1.

Referring now to the accompanying drawings, the variable electrical resistor or potentiometer therein illustrated comprises a main frame having end plates 11 in which is journaled a control shaft 12. Carried by the control shaft 12, and connected for rotation therewith, is the resistance element 13 and a cam 14 which is thus fixed coaxially with respect to the resistance element 13. Pivotally mounted about the axis of rotation of the driving spindle 12 is a contact-carrying member 15 which, in the embodiment shown, comprises four arms and four contacts 16 which are pressed into engagement with the resistance 13 by means of radially extending fiat leaf springs 17. Pivotally mounted, as at 18, at a suitable point on one of the end-plates 11 is an arm 2,866,050 Patented Dec. 23, 1958 19 having a cam-follower 20 which is pressed into engagement with the circumference of cam 14 by a tension spring 21 connected between the free end of the pivoted arm 19 and a fixed point 22 on one of the end plates 11. A short link 23 is connected from a suitable point on the arm 19 to the contact-carrying member 15.

It will be seen that as the control shaft 12 is rotated, together with it the resistance element 13 and the cam 14, the pivoted arm 19 will be angularly displaced about its pivot 18 by reason of the engagement of the cam-follower 20 with the specially shaped circumference of cam 14, and in so doing will cause the contact-carrying member 15 to be correspondingly angularly displaced about the axis of rotation of the control shaft 12, thereby advancing or retarding the points of contact of the sliding contacts 16 with the resistance element 13 in relation to the points which would be engaged if the cam 14 were of uniform radius. Hence, by suitably shaping the circumferential profile of cam 14, any desired relationship between shaft displacement and resistance variation may be obtained, so that the potentiometer can be made to follow any desired mathematical function or non-linear relationship. Further factors affecting the amount of non-linearity, in addition to the circumferential shape of cam 14, are, of course, the distance between the pivot point of the arm 19 and the point at which the link 23 is connected thereto, and also the point at which the link 23 is connected to the contact-carrying member 15, and all these dimensions must be suitably chosen to give the desired non-linear response.

I claim:

1. An adjustable resistor comprising an annular re sistance element; a contact member angularly displaceable about an axis concentric with said resistance element, said contact member including a contact slidingly engaging said resistance element; a revoluble control shaft connected to produce relative movement between said contact and said resistance element during rotation of said shaft; a generally circular cam concentrically mounted and fixedly positioned with respect to said resistance element; a cam follower circumferentially engaging said cam; and linkage means connecting said cam follower and said contact member for displacing said contact in accordance with the circumferential shape of said cam during the course of said relative movement, the radius of said cam being different at different portions of its circumference to produce a predetermined non-linear relationship between angular displacements of said shaft and the position of engagement of said contact with said resistance element.

2. An adjustable resistor, comprising a control shaft; an annular resistor carried concentrically by said shaft for rotation therewith; a generally circular cam c0- axiallyfixed to said shaft for rotation therewith, the circumference of said cam being of non-uniform radius and shaped to produce a predetermined non-linear relationship for resistance variation with respect to angular displacement of said shaft; a cam follower circumferentially engaging said cam during rotation thereof; a contact member slidingly engaging said resistor during rotation thereof, said contact member being circumferentially displaceable with respect to said annular resistor; and linkage means connecting said cam follower to said contact member to vary the position of said contact member in accordance with the shape of said cam during rotation of said resistor by said shaft.

3. An adjustable resistor comprising a revoluble control shaft; an annular resistance element concentrically fixed to said shaft for rotation therewith; a generally circular cam fixed to said shaft for rotation therewith along with said resistance element; a contact member angularly displaceable about the rotational axis of said shaft, said contact member carrying a contact which slidingly engages said resistance element; an arm pivoted for angular displacement about a fixed axis; a cam follower carried by said arm and circumferentially engaging said cam during rotation thereof; spring means acting on said arm and yieldingly urging said cam follower into engagement with said cam; and a link connecting said arm to said contact member, the radius of said cam being different at different portions of its circumference to pro- 10 ,226

duce a predetermined non-linear relationship between angular displacements of said shaft and the position of engagement of said contact with said resistance element.

References Cited in the file of this patent UNITED STATES PATENTS Dewan Apr. 29, 1952 Mucher Apr. 20, 1954 

